The present invention relates to railway freight car coupling systems, and, more particularly, to draft gear assemblies used in conjunction with draft sills and couplers in railway freight cars.
Draft gear assemblies are utilized as part of the connection between the couplers at the ends of adjoining railway freight cars and the draft sills at the ends of the railway freight cars. The draft sills are commonly cast steel or fabricated steel structures that are mounted at the ends of the center sills of the railway freight car. The draft sills have a pair of front stops and a pair of rear stops, with a draft gear pocket formed between the front and rear stops. A draft gear assembly is received in the draft gear pocket.
Each draft gear assembly is connected to a coupler shank, with coupler heads of adjacent rail cars connected to form the train. The train may be up to one hundred or more cars long and drawn by one or more locomotives. Typically, there is a limited amount of slack or free movement allowed between the cars; typically there is about two (2) inches of slack between adjacent railway freight cars. This slack allows the railway freight cars limited movement toward each other in response to buff or impact events which usually occur during train deceleration and away from each other in response to draft events which usually occur during train acceleration.
Train deceleration usually subjects the couplers of the cars to buff impacts, and train acceleration usually subjects the couplers of the cars to draft impacts. These impacts are transmitted from the couplers to the draft gear assemblies to the rail car body. That is, as the couplers are pulled or pushed, the movement is translated to the freight car body through the draft gear assemblies. Typical draft gear assemblies include a draft sill housing in which all the components of the draft gear assembly are fitted in what is deemed a draft gear pocket, a yoke element within the draft sill that is connected to the coupler through a pin or key, a coupler follower and a draft gear, as well as other elements. Generally, the coupler follower is positioned against or closely spaced from the butt end of the coupler in the draft gear pocket, within the yoke. The draft gear is positioned between the coupler follower and the rear stops of the draft sill; other elements, such as a wedge, may be interposed between the draft gear and the coupler follower.
In buff events, the butt end of the coupler moves inward against the coupler follower toward the rear stops of the draft sill. As the coupler and coupler follower are moved rearward, the shock of the movement is transferred to the draft gear. The draft gear typically absorbs and dissipates some of the energy from this shock through friction.
In draft events, slack is taken up between adjacent cars beginning at one end of the train and ending at the other end of the train. As a result of the slack being progressively taken up, the speed differences between the railcars increases as the slack at each coupler pair is taken up, with a resultant increase in buff and draft impacts on the couplers. For instance, during locomotive acceleration of a 100 car train from rest there may be a total of 200 inches of slack between the 100 pairs of couplers in the train. This slack is taken up progressively, coupler pair by coupler pair. When the 2 inch slack in the coupler pair joining the last car to the train is taken up the next to the last car may be moving at a speed of 4 miles per hour. The slack in the last coupler pair is taken up very rapidly and the last two cars are subjected to a very large impact capable of injuring the lading or the car.
Various types of draft gear assemblies have been proposed and used. Some draft gear assemblies employ mechanical springs and steel friction members held in a steel housing that is received in a yoke. Other draft gear assemblies employ elastomer springs. However, those employing a steel housing add to the weight of the railcar. Those employing elastomer springs may be difficult to install and remove from standard draft sills.
In exceptionally heavy duty railway freight car service, such as in captive mining service wherein individual gross railway car loading may exceed 286,000 pounds, there have been concerns relating to the performance of draft gear assemblies. There is a limited amount of space available in the railway freight car draft gear pocket to accommodate the draft gear assembly. Accordingly, the draft gear assembly and its inherent performance are limited by the space available in the draft gear pocket. In typical railway freight cars, the draft gear pocket cross sectional dimensions are approximately 8 and ⅞ inches by 12 and ½ inches, for a typical cross section of approximately 111 square inches. The force per unit area to which the draft gear assembly is exposed is accordingly the compressive pound force divided by the cross sectional dimension. For example, a 300,000 pound buff force divided by the nominal 111 square inch cross sectional dimension would result in a force on the draft gear assembly of 2702 pounds per square inch. The unit loading is prescribed by the physical dimensions of the draft gear pocket. Accordingly, it is an object of the present invention to provide reduced unit loading within the standard draft gear pocket physical dimensions.